The present invention generally relates to the field of electronic engine control circuits for use in the synchronization and timing of engine control functions such as fuel injection and spark ignition occurrence. More particularly, the present invention relates to the use of engine crankshaft and engine camshaft electronic position sensors for deriving cylinder identification information as well as precise engine crankshaft position information.
For electronic control of the operation of a multi-cylinder internal combustion engine, typically it is necessary to identify when a piston of a reference cylinder of a multi-cylinder engine is at a particular position in its reciprocal cycle. Typically this cylinder identification information is used to insure the proper sequencing of fuel into each cylinder and/or to insure the proper sequencing of a spark occurrence signal to each cylinder. The cylinder piston position directly corresponds to the angular position of the engine camshaft which is rotated at one half of the rotational speed of the engine crankshaft which supplies the reciprocal driving movement to the cylinder piston. Many types of cylinder identification techniques are known and some of these are described in detail in the copending U.S. patent application referred to above. That application describes an additional cylinder identification technique in which the cylinder piston position, which is directly related to the engine camshaft angular position, is determined by two camshaft sensors sensing the passage of a plurality of camshaft projections and determining the angular position of the camshaft by determining which of the two sensors is presently producing a camshaft position pulse and which of the sensors previously produced a camshaft sensor pulse.
In electronic engine control it is also necessary to provide very accurate information with regard to the angular rotational position of the engine crankshaft. Typically, the required resolution accuracy cannot be obtained by merely using engine camshaft sensors since the physical dimensions of the engine generally prohibit the use large diameter rotary bodies attached to the engine camshaft. In addition, when sensing engine crankshaft positions, if a plurality of projections are provided on the engine crankshaft, then some technique to distinguish between the pulses produced by these plurality of projections must be developed. In some instances, one of a plurality of the engine crankshaft projections is formed in a special manner so that it serves as a reference crankshaft projection. However, this means that almost a full revolution of the engine crankshaft may have to occur before enough information is gathered to properly identify the true angular position of the engine crankshaft. During the start-up of an automobile engine, this time delay would be detrimental.
In some electronic engine control systems utilizing crankshaft position sensors, profile (proximity) sensors are utilized to obtain rising and falling signal transitions each of which represents a different desired rotational position of the engine crankshaft corresponding to the widely spaced rising and falling edges of the peripheral crankshaft projections. While this type of signal is readily usable by engine control microprocessors, the cost of such profile sensors is typically far more than the cost of reluctance sensors which merely produce identical polarity transitions at desired predetermined engine crankshaft rotational positions. In addition, such profile sensors generally incorporate electronics into the sensor body and this electronics is subject to extreme environmental conditions which inherently affect the reliability of such sensors.